Akhtar told friends he lunged at Azim with the kitchen knife in revenge for being “snaked" - a slang term for insulted.

Det Supt Mark Payne said the case sent out stark warnings over the danger of carrying knives in public.

He said: “This is a terribly tragic case. Azim had just enrolled on a sports course and was hoping it would pave the way for a PE teaching career.

"He chose to attend a college away from his home in Billesley, free from distractions and what he saw as negative influences - but whilst travelling to college he was fatally attacked.

“These two teenagers clearly didn’t get on - though quite what caused the spat is unclear - and it came to a head when they saw each other on the bus that fateful morning.

“Had Akhtar not been carrying a knife they may well have had a bit of a dust up and most likely walked away with a few cuts and bruises; who knows, it may well have settled their differences.

“But carrying a knife, or indeed anything that could be used as a weapon, is a game changer: if you set foot in public with a knife you not only endanger other people’s lives but also your own. If someone with a knife gets caught up in a row or scuffle there’s every chance that knife could be used to injure or kill - and may well be used against the carrier.

“Anyone using a knife in anger can expect to waste much of their life behind bars."

Azim boarded the No 2 bus in Yardley Wood Road, near Swanhurst Lane, at around 8.25am and within moments Akhtar - who was sat at the rear - began hurling abuse. CCTV then showed him pulling on a pair of black gloves.

Fellow passengers told how Akhtar - a frequent bus passenger - shouted “what you doing on my bus... I’m going to deal with you" and “let’s go to town" which is understood to mean let’s have a fight.

Azim shrugged off the taunts and minutes later got off at his usual stop at the junction with Wake Green Road.

Witnesses describe how Akhtar, from Glen Rise in Kings Heath, shoved his way past people standing in the aisle to reach Azim and, as he stepped off, stabbed him in the chest.

Azim initially ran off but after a short distance slumped to the ground. A doctor tried reviving him as he lay on the pavement but despite the best efforts of paramedics he later died in hospital.

Akhtar - known amongst associates as ‘Ace’ - phoned a friend on the bus saying “I think I got him but there’s no blood on my weapon" before attending a youth course later that morning. Witnesses said Akhtar, now aged 18, acted normally and didn’t appear nervous or anxious.

Police made numerous arrest attempts at addresses known to Akhtar and he handed himself in to Birmingham Central Police station the following morning.

Det Supt Payne, said: “Just two weeks before the incident Akhtar made threats to a friend that he intended to stab Azim - and during interview other associates told how they suspected him of carrying weapons in the past.

“We need to know information like this. It could save a life, it’s that important. If anyone suspects a person of carrying a knife, or any other kind of weapon, then call police on 101 - you can speak to us in confidence and don’t have to leave your name.

A joint statement issued by West Midlands Police on behalf of Azim’s family told how he left for college “smiling and full of hope" - but was never to return home.

It reads: “We still feel lost and heartbroken over the loss of Azim... a mother should never have to bury her son. Nothing will ever bring our boy back but some peace may be found knowing the person who killed him isn’t free to walk the streets carrying a knife, putting further lives at risk. To us this behaviour is so unacceptable.

“An innocent boy’s life was lost while on his way to his first day at college. He left that morning smiling and full of hope for his future. We will never forget the way Azim lost his life. We will always miss him and love him."